Judge Crane McClennen said that with that decision, the commission “erred and abused its discretion.”

The commission requires utilities to get 15 percent of their electricity from renewable sources such as wind and solar by 2025. When passed in 2006, those rules excluded trash burning as a form of renewable energy.

Then in 2011 and again in 2012, commissioners granted Mohave permission to count the electricity from a trash incinerator toward its goals.

Democrats Paul Newman and Sandra Kennedy both voted against the trash burning last year. Both lost re-election bids. Republicans Bob Stump, now the chairman, Gary Pierce and Brenda Burns voted in favor of the project.

Stump said the commission is considering an appeal of the decision.

“I’m disappointed the court decided to substitute its judgement for the judgement of five elected commissioners, the elected board of Mohave Electric Cooperative and our professional staff with hundreds of years of combined experience,” he said. “The Obama administration’s own (Environmental Protection Agency) and over 20 states classify waste energy as renewable energy. The Maryland governor, arguably the most liberal governor in the nation, signed legislation treating waste energy as renewable energy.”

He said the regulators are interested in the most cost-effective power sources available, and that the evidence presented to them suggested the project should be approved.

Sierra Club officials said the incinerator would contribute to the already poor air quality in metro Phoenix, and also provide a loophole for utilities to skirt the renewable energy rules.

“These are the last places you should be burning trash because you already have air-quality problems,” said Sandy Bahr, director of the Sierra Club’s Grand Canyon Chapter.

“The whole intent of the renewable-energy standard is to promote clean, renewable energy,” she said. “The concern was for this specific project (and its air pollution), but also what it could do to the renewable-energy standard by weakening it and getting around the definitions.”

The commission said Mohave could count 90 percent of the energy from burning trash toward the renewable goals, not all of it, because not everything in the trash is renewable. The Sierra Club, represented in court by the Arizona Center for Law in the Public Interest, said that much credit was too much.

The trouble with trash is that it contains “biogenic” material, such as paper, yard trimmings and food waste, and “non-biogenic” material like plastics and rubber. Non-biogenic material is not renewable and thus doesn’t fit the definition of renewable energy.

The sample that Mohave provided to the commission contained 82 percent biogenic material and 12 percent non-biogenic material. Six percent of the material was not combustible.

Bahr said that the commissioners were only giving Mohave the 90 percent credit, rather than a smaller percent as originally proposed, to help the power plant developers make the economics work out, and that the figure was not supported by evidence.

The facility would have a capacity of 11 megawatts, according to commission filings. That is enough electricity to supply about 2,750 homes at once while a plant is running.

It is unclear if the commission, Mohave, or the startup company that would have run the trash power plant, Reclamation Power Group, will appeal the decision.

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